Autumn (September to early November) is the optimal season to visit Běijīng as the weather is gorgeous and fewer tourists are in town. Local Beijingers describe this short season of clear skies and breezy days as tiāngāo qìshuǎng (literally ‘the sky is high and the air is fresh’). In winter, it’s glacial outside (dipping as low as -20°C) and the northern winds cut like a knife through bean curd. Arid spring is OK, apart from the awesome sand clouds that sweep in from Inner Mongolia and the static electricity that discharges everywhere. Spring also sees the snowlike liǔxù(willow catkins) wafting through the air and collecting in drifts. From May onwards the mercury can surge well over 30°C. Běijīng simmers under a scorching sun in summer (reaching over 40°C), which also sees heavy rainstorms late in the season. Maybe surprisingly, this is also considered the peak season, when hotels typically raise their rates and the Great Wall nearly collapses under the weight of marching tourists. Air pollution can be intolerable in both summer and winter.